In recent years, carbon nanotubes (hereinafter, also referred to as “CNTs”) have been attracting attention as materials having excellent electrical conductivity, thermal conductivity, and mechanical characteristics.
However, CNTs are fine tubular structures having nanometer-size diameters, which makes handling and processing of individual CNTs difficult. In consideration of this, it has been proposed, for example, that a plurality of CNTs may be assembled into a film shape to form a carbon nanotube film (hereinafter, also referred to as a “CNT film”), which is sometimes also referred to as “buckypaper”, and this CNT film may be used as a conductive film or the like. More specifically, it has been proposed that a CNT film formed by removing a solvent from a carbon nanotube dispersion liquid (hereinafter, also referred to as a “CNT dispersion liquid”) containing the solvent and CNTs may be used as a component (for example, a conductive film or catalyst layer) of an electrode in a solar cell, touch panel, or the like. Such CNT films are attracting interest as film-shaped materials having excellent electrical conductivity, thermal conductivity, and mechanical characteristics.
However, there is demand for further improvement of properties of CNT films (for example, electrical conductivity, thermal conductivity, and mechanical characteristics). In order to improve such properties of CNT films, it is important to favorably assemble CNTs having excellent characteristics in high-density. In one example, PTL 1 proposes a technique for obtaining a high-density CNT film by forming a sheet using a highly-dispersed dispersion liquid obtained by applying a high pressure of 100 MPa to 280 MPa to a CNT dispersion liquid, and then performing rolling of the resultant CNT sheet with a pressing pressure of 0.01 ton/cm2 to 100 ton/cm2.